<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
    <style>
        #first{
            width: 600px;
            height: 600px;
            background-color: #c91212;
            display : flex;
            align-items: center;
            justify-content: center;

        }
        #second {
            width: 400px;
            height: 400px;
            background-color: #30dd89;
            display: flex;
        }
    </style>
</head>
<body>
    
    <div id="first">
        <div id="second">

        </div>
    </div>
</body>
</html>